The present disclosure is generally related to touch screens, and more particularly to systems and methods for determining a touch position on a touch screen.
U.S. Pat. No. 5,951,397 to Dickinson, entitled “Gaming Machine and Method Using Touch Screen,” described a gaming machine having a touch screen applied to an outer face of a cathode ray tube (CRT). The touch screen comprised a transparent panel (touch panel) which was curved and shaped to correspond to the curvature and shape of the CRT screen surface to which it was applied. U.S. Pat. No. 5,951,397 explains that one type of touch panel that could be used was fitted with a number of relatively short (e.g., one-inch or so in length), mostly linear, spaced-apart electrodes arranged in one to three spaced-apart, peripheral lines along the perimeter of the touch screen. A controller board was coupled to the touch panel and included a touch screen processor, an analog-to-digital converter (ADC) and other electronic components which were appropriately connected with the electrodes so that the location at which a person touched the screen could be sensed by the electrodes. Then, a signal corresponding to the location was generated which was further used to execute specific commands for playing a game. A message was generated by the CRT display beneath the touch panel to inform the player of the command corresponding to the location on the touch panel.
U.S. Pat. No. 5,796,389 to Bertram et al., entitled “Reduced Noise Touch Screen Apparatus and Method,” described a touch screen apparatus including four electrodes, each in the shape of a conductive bus bar, that were positioned along the edges of the touch screen. Four conductive wires were coupled to electrodes. The four electrodes could be silk screen directly onto a screen of a display (e.g., a CRT), and a conductive coating could be applied over the electrodes and the screen of the display. A sinusoidal signal was applied to the electrodes via the conductive wires. When a person touched the conductive coating, a small amount of current would flow from the electrodes, through the person's body, and to ground. The amount of current flowing from a given electrode was generally dependent upon the distance of the touch position from the given electrode. Thus, the amount of current flowing through each of the electrodes was used to calculate a position of a touch.
Four operational amplifiers (op amps) were used to sense the four currents flowing from the four electrodes. The outputs of the four op amps were filtered by four corresponding bandpass filters that acted to reject noise. The outputs of the four bandpass filters were then provided to an ADC, and an output of the ADC corresponding to the outputs of the four bandpass filters was provided to a central processing unit (CPU).
The CPU then determined when a touch occurred by detecting peaks in the outputs from the bandpass filters, and determining whether the peaks exceeded a threshold. When a touch was detected, the system took four samples from each of the four outputs of the bandpass filters. Then, these samples were used to calculate a touch position. Next, the calculated touch position was adjusted using predetermined parameters to account for nonlinear characteristics of the touch screen system.